8. 过滤器模式

过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种设计模式，这种模式允许开发人员使用不同的标准来过滤一组对象，通过逻辑运算以解耦的方式把它们连接起来。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。

实现

我们将创建一个 Person 对象、Criteria 接口和实现了该接口的实体类，来过滤 Person 对象的列表。CriteriaPatternDemo 类使用 Criteria 对象，基于各种标准和它们的结合来过滤 Person 对象的列表。

步骤 1

创建一个类，在该类上应用标准。

package org.example.FilterPattern;
/**
 * 人
 */
public class Person {
   private String name;
   private String gender;
   private String maritalStatus;
   public Person(String name,String gender,String maritalStatus){
      this.name = name;
      this.gender = gender;
      this.maritalStatus = maritalStatus;    
   }
   public String getName() {
      return name;
   }
   public String getGender() {
      return gender;
   }
   public String getMaritalStatus() {
      return maritalStatus;
   }  
}

步骤 2

为标准（Criteria）创建一个接口。

package org.example.FilterPattern;
import java.util.List;
/**
 * 标准
 */
public interface Criteria {
   public List<Person> meetCriteria(List<Person> persons);
}

步骤 3

创建实现了 Criteria 接口的实体类。

package org.example.FilterPattern;
import java.util.ArrayList;
import java.util.List;
/**
 * 标准的女
 */
public class CriteriaFemale implements Criteria {
   @Override
   public List<Person> meetCriteria(List<Person> persons) {
      List<Person> femalePersons = new ArrayList<Person>(); 
      for (Person person : persons) {
         if(person.getGender().equalsIgnoreCase("FEMALE")){
            femalePersons.add(person);
         }
      }
      return femalePersons;
   }
}

package org.example.FilterPattern;
import java.util.ArrayList;
import java.util.List;
/**
 * 标准的男性
 */
public class CriteriaMale implements Criteria {
   @Override
   public List<Person> meetCriteria(List<Person> persons) {
      List<Person> malePersons = new ArrayList<Person>(); 
      for (Person person : persons) {
         if(person.getGender().equalsIgnoreCase("MALE")){
            malePersons.add(person);
         }
      }
      return malePersons;
   }
}

package org.example.FilterPattern;
import java.util.ArrayList;
import java.util.List;
/**
 * 标准单
 */
public class CriteriaSingle implements Criteria {
   @Override
   public List<Person> meetCriteria(List<Person> persons) {
      List<Person> singlePersons = new ArrayList<Person>(); 
      for (Person person : persons) {
         if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){
            singlePersons.add(person);
         }
      }
      return singlePersons;
   }
}

package org.example.FilterPattern;
import java.util.List;
/**
 * 或者标准
 */
public class OrCriteria implements Criteria {
   private Criteria criteria;
   private Criteria otherCriteria;
   public OrCriteria(Criteria criteria, Criteria otherCriteria) {
      this.criteria = criteria;
      this.otherCriteria = otherCriteria; 
   }
   @Override
   public List<Person> meetCriteria(List<Person> persons) {
      List<Person> firstCriteriaItems = criteria.meetCriteria(persons);
      List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persons);
      for (Person person : otherCriteriaItems) {
         if(!firstCriteriaItems.contains(person)){
           firstCriteriaItems.add(person);
         }
      }  
      return firstCriteriaItems;
   }
}

package org.example.FilterPattern;
import java.util.List;
/**
 * 和标准
 */
public class AndCriteria implements Criteria {
   private Criteria criteria;
   private Criteria otherCriteria;
   public AndCriteria(Criteria criteria, Criteria otherCriteria) {
      this.criteria = criteria;
      this.otherCriteria = otherCriteria; 
   }
   @Override
   public List<Person> meetCriteria(List<Person> persons) {
      List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);     
      return otherCriteria.meetCriteria(firstCriteriaPersons);
   }
}

步骤4

使用不同的标准（Criteria）和它们的结合来过滤 Person 对象的列表。

package org.example.FilterPattern;
import java.util.ArrayList;
import java.util.List;
/**
 * 标准模式演示
 */
public class CriteriaPatternDemo {
   public static void main(String[] args) {
      List<Person> persons = new ArrayList<Person>();
      persons.add(new Person("Robert","Male", "Single"));
      persons.add(new Person("John","Male", "Married"));
      persons.add(new Person("Laura","Female", "Married"));
      persons.add(new Person("Diana","Female", "Single"));
      persons.add(new Person("Mike","Male", "Single"));
      persons.add(new Person("Bobby","Male", "Single"));
      Criteria male = new CriteriaMale();
      Criteria female = new CriteriaFemale();
      Criteria single = new CriteriaSingle();
      Criteria singleMale = new AndCriteria(single, male);
      Criteria singleOrFemale = new OrCriteria(single, female);
      System.out.println("Males: ");
      printPersons(male.meetCriteria(persons));
      System.out.println("\nFemales: ");
      printPersons(female.meetCriteria(persons));
      System.out.println("\nSingle Males: ");
      printPersons(singleMale.meetCriteria(persons));
      System.out.println("\nSingle Or Females: ");
      printPersons(singleOrFemale.meetCriteria(persons));
   }
   public static void printPersons(List<Person> persons){
      for (Person person : persons) {
         System.out.println("Person : [ Name : " + person.getName()
            +", Gender : " + person.getGender()
            +", Marital Status : " + person.getMaritalStatus()
            +" ]");
      }
   }      
}